Both paging systems and mobile telephone systems are widely used forms of communication. These systems allow individuals to keep in contact while away from a fixed telephone.
Existing paging systems are one-way radio communication systems. Typically, a paging system includes a centrally located control unit and a plurality of mobile pagers carried by individuals within a region. When a paging party wishes to contact an individual carrying a pager, the paging party dials the telephone number of the pager. The call is routed to the central control unit, which may be an automatic device or a human-operated device (for example, a telephone answering service). The paging party can either leave a voice message for the person being paged or key in the paging party's telephone number or other message. The central control unit will then transmit a radio signal addressed to the appropriate pager. Upon receipt of this radio signal, the receiving pager will either prompt the individual to call the central control unit to receive a message or display the calling telephone number or other message. Current paging systems are national in scope and are expected to become international in the near future.
Many prior an mobile telephone systems are cellular in nature. That is, the service area of the company providing the telephone system is divided into cells or regions. A central switching office connected to each cell allows mobile telephones within the cell to be contacted. Typically, an individual places a telephone call to an individual cellular phone, which is routed to the cellular central office. The central office signals the called party either directly or through a number of other cells and completes the call if the called party answers the called mobile telephone.
Many existing cellular telephone systems suffer from the problem that a cellular telephone cannot receive telephone calls if it is outside its local cellular service area. This is so because none of the cell transmitters within the local network has enough range to establish communication with the cellular telephone. Another problem is that if the cellular telephone is turned off or the user is away from the cellular telephone when a call is made to that device, the call will be missed. Another problem is that the cellular telephone user typically pays for incoming as well as outgoing calls. If an unwanted call is made to the cellular telephone, the cellular telephone user must pay for it.
Several solutions have been proposed to remedy the problem of contacting a cellular telephone that is outside of its local cellular service area. One system maintains a database that stores the location of each cellular telephone. When a cellular telephone makes a call, the database stores the calling telephone number and cell location of the cellular telephone in order to locate that telephone when it is called in the future. Alternatively, each cellular telephone can be programmed to automatically send a signal to the database to update the database instead of waiting for each telephone to make an actual telephone call. Database systems of this type are undesirable because there is a relatively high overhead in creating and maintaining such a database. Further, the maintenance of such databases raise privacy and security issues for individual cellular telephone users.
An alternative to the database system is described in U.S. Pat. No. 5,117,449 to Metroka et al. The system described therein combines a paging receiver with a cellular telephone. To contact a pager/cellular telephone outside of the local cellular service area, a calling telephone places a first call to a paging control unit, which pages the pager/cellular telephone and transmits the telephone number of the calling telephone to the pager portion of the pager/cellular telephone. If desired, the cellular telephone user may then place a second call back to the calling telephone using the telephone number. While this system relieves some of the problems in locating distant cellular telephone users, it is undesirable because it requires a separate telephone call to be placed by the pager/cellular telephone user to connect with the calling party.